The present invention relates generally to printers and, more particularly, to a method for determining vertical misalignment between print heads.
Many printers include print heads which are mounted on a carriage for movement across a paper path during printing operations. An ideally assembled printer includes print heads which are mounted in predetermined positions so as to place the print head nozzles in predetermined desired positions. However, mechanical tolerances and manufacturing techniques rarely provided for positioning of the print heads exactly at the predetermined desired positions. Accordingly, for any given printer their will typically be both a horizontal misalignment between print heads and a vertical misalignment between print heads. Many techniques for determining horizontal and vertical misalignment between print heads are known, but simpler techniques are always more desirable.
While U.S. Pat. No. 5,796,414 discloses the printing and scanning of a diagonal test pattern, each print head prints a bunched sequence of diagonal lines and the sequences printed by the print heads do not overlap. Complex calculation techniques are used to evaluate the diagonal pattern.
Accordingly, it would be advantageous to provide a technique for determining vertical misalignment between print heads where a horizontal misalignment between the print heads is already known.
In one aspect, in a printer including first and second print heads mounted for movement across a paper path along a defined horizontal axis, a method for determining vertical misalignment between the print heads along a defined vertical axis which extends substantially perpendicular to the horizontal axis is provided. The method involves the steps of: (a) printing a test pattern of first and second alternating slanted blocks extending horizontally across a media, the first slanted blocks printed by the first print head and the second slanted blocks printed by the second print head, a known edge angle of the first and second slanted blocks being substantially the same; (b) moving a sensor horizontally over the test pattern and producing an output signal therefrom; (c) identifying edges of the first slanted blocks and the second slanted blocks based upon the sensor output signal; and (d) determining vertical misalignment of the first and second print heads based upon the edges identified in step (c), the known edge angle, and a known horizontal misalignment of the first and second print heads.
In another aspect, in a printer including first and second print heads mounted for movement across a paper path along a defined horizontal axis, a method for determining misalignment between the print heads along a defined vertical axis which extends substantially perpendicular to the horizontal axis is provided. The method involves the steps of: (a) printing a test pattern of a plurality of first slanted blocks and a plurality of second slanted blocks, the first slanted blocks and second slanted blocks alternating and extending horizontally across a media, the first slanted blocks printed by the first print head and the second slanted blocks printed by the second print head, a known edge angle of the first and second slanted blocks being substantially the same; (b) moving a sensor horizontally over the test pattern and producing an output signal therefrom; (c) obtaining sample data points of the sensor output signal at a known sampling rate as the sensor moves at a known speed; (d) calculating using the sample data points a first center of a given first slanted block, a second center of an adjacent second slanted block, and a third center of a next first slanted block; (e) calculating a horizontal offset as a function of the first, second and third centers; and (f) determining vertical misalignment of the first and second print heads based upon the calculated horizontal offset of step (e), the known edge angle, and a known horizontal misalignment of the first and second print heads.
In a further aspect, in a printer including first and second print heads mounted for movement across a paper path along a defined horizontal axis, a method for determining misalignment between the print heads along a defined vertical axis which extends substantially perpendicular to the horizontal axis is provided. The method involves the steps of: (a) printing a test pattern of a plurality of first slanted blocks and a plurality of second slanted blocks, the first slanted blocks and second slanted blocks alternating and extending horizontally, the first slanted blocks printed by the first print head and the second slanted blocks printed by the second print head, a known edge angle of the first and second slanted blocks being substantially the same; (b) moving, at a known speed, a sensor horizontally over the test pattern and producing an output signal therefrom; (c) determining vertical misalignment of the first and second print heads as a function of amplitude of the sensor output signal, the known speed, the known edge angle, and a known horizontal misalignment of the first and second print heads.